Answers

Using it with a hydronic baseboard system adds complexity and distribution losses without any gains over electric baseboard heaters.

As I explained in my answer to Brittany Sims of Oregon, electrical energy has about three times the carbon footprint per unit of energy that gas has. So while there are many household tasks, such as lighting, that require electrical energy, heating is more efficiently powered by gas (or in absence of gas, oil-but it is typically less efficient and not as "clean" as gas).

My recommendation would therefore be to use a tankless gas heater to run your baseboard heating system. If you do not have gas in your cottage, consider a propane tank, or best of all, install a solar hot-water system with a small electric backup.

Building a baseboard hydronic heating system

To build a baseboard hydronic heating system, you will need

a pump,

a manifold,

a control system, and

the tankless heater of your choice.

If you add solar, you will also need solar collectors and a solar storage tank.

There are several companies in the Northeast that will pre-assemble a set of everything you need, making the install easy for you or quick for your contractor. Both Radiantec and Radiant Company offer these packages, but Radiantec will not allow the use of tankless heaters in their system.

Electric heat pump

If it is not possible to use gas and your location is not right for solar-so that you are forced to go the electrical route-the best way to heat your home is to use an electric heat pump.

Heat pumps do not "burn" electricity to produce heat; they move heat. They are basically air-conditioners running backwards. For each unit of electrical energy expended, they move about 2.5 units of heat energy into your house.

As a result, they would conserve 40-60% of the energy used by a system with an electric tankless water heater or electric baseboards.

There are two problems:

Maine has very low outside air temperatures in winter.

There are few air-to-water heat pumps on the U.S. market that tie into a hot-water heating system; you may have to switch to forced-air and a standard air-to-air heat pump.

Traditional heat pumps require an outside air temperature of about 30 degrees Fahrenheit, but some Northeastern companies have vastly lowered this barrier in recent years. Others import heat pumps from cold Scandinavia that faces the same problem. You will need to buy from a manufacturer that specializes in your climate, like Save Energy Maine. (Save Energy Maine also sells air-to-water heat pumps that would work with your baseboard heaters.)

You can also see what other providers are available in your area from Furnace Compare.

If these systems end up being too expensive, I would recommend researching oil as your next option.